Some motor vehicles are equipped with so-called automatic start-stop systems that shut off the engine at standstill in order to save energy. A few motor vehicles have a similar functionality while driving. In such a driving mode, the drive train is decoupled from the wheels of the motor vehicle and either set to idle speed or completely shut off. Such a driving mode is colloquially referred to as coasting. While driving, electrical consumers of the motor vehicle are supplied with electric energy by a generator that is driven by the engine. If the engine is completely shut off in the coasting mode, however, the generator can no longer generate energy. The electrical consumers therefore have to be supplied with electric energy by the motor vehicle battery.
Certain electrical consumers of a motor vehicle are particularly relevant to the safety of a moving motor vehicle. These include, among other things, electrically operated power-steering systems, displays in the motor vehicle, as well as certain sensors such as certain electric actuators. It is therefore important to ensure a particularly high operational safety of a rolling motor vehicle in case the engine is shut off.
DE 199 57 478 A1 discloses a two-battery system with a starter, a generator, a starter battery, an electric system battery, consumers specific to the electric system and consumers relevant to the starter. A first electronic pole binder is arranged between the starter and the starter battery and a second electronic pole binder is arranged between the starter and the electric system battery. Before a starting process is initiated, the control unit of the electric system checks the state of charge of the electric system battery and the starter battery. If it is determined that the electric system battery is charged and the starter battery is discharged, a power switch is closed by the control unit of the electric system. In this way, the electric system battery can supply consumers relevant to the starter in the starting phase.